I wonder this too. I tried scraping iOS App reviews from Apple's server and I didn't get far before my IP was blocked.
Probably just used the previews (makes sense, songs tend to keep their rhythm throughout).
Lots of industrial metal has a drawn out start before the actual song lol
Previews don't start at 0:00 but at a place selected by the artist give the best quick impression possible. Of course, I don't know what they've done with the "old" catalog.